The present invention relates generally to heating apparatus, and more particularly relates to fuel-fired water heating appliances such as water heaters and boilers.
Conventional fuel fired water heaters are typically provided with "up-flow" firing configurations in which upper and lower tube sheet structures are secured at the top and bottom ends of the metal storage tank portion of the water heater. The open upper and lower ends of a spaced series of submerged vertical heating flues are respectively secured to these upper and lower tube sheets and receive an upward throughflow of hot combustion gases generated by a fuel burner structure disposed beneath the lower tube sheet. These upwardly flowing combustion gases serve to heat water stored in the tank for on-demand outflow therefrom to the various plumbing fixtures served by the water heater. The combustion gases upwardly exiting the vertical flues are discharged to ambient through a suitable vent pipe.
Despite the wide acceptance and use of this upflow configuration in fuel-fired water heaters, it presents a variety of well known problems, limitations and disadvantages. For example, the single upward pass of hot combustion gases through the tank water tends to provide a relatively low combustion gas-to-water heat exchange efficiency rate.
Additionally, various fabricational complexities associated with conventional upflow water heaters tend to undesirably add to their overall manufacturing cost. As an example, the necessity of providing both top and bottom tube sheets requires that numerous welds be formed to operatively secure both the top and bottom ends of the flues to their associated tube sheets. Moreover, the presence of the bottom tube sheet complicates the formation of the usual outer jacket insulation structure that encapsulates the storage tank. During the placement of the insulation around the tank, auxiliary insulation stop structures must typically be utilized. Also, a bottom skirt structure is normally required in conjunction with the bottom end burner used in these upflow water heaters.
In response to these problems associated with upflow water heaters, various solutions have heretofore been proposed in the prior art, including the construction of water heaters in downflow configurations in which the burner is mounted on the top of the water heater, and the hot combustion gases generated by the top-mounted burner are downwardly flowed through a series of vertical flues submerged within the storage tank. While this reversed configuration typically positions the burner on top of the tank, it still requires considerable welding since both an upper tube sheet and a lower tube sheet are needed. Additionally, insulation stops are still required, due to the presence of the lower tube sheet, and the single pass of hot combustion gases through the tank water keeps the overall combustion gas-to-water heat exchange efficiency at a relatively low level.
Another approach used in the prior art in an attempt to reduce the various problems associated with upflow firing configurations in water heaters is to provide what may be designated a horizontal, multi-pass firing configuration. Under this approach, a multi-pass immersion heater structure is extended horizontally into the storage tank interior through an side wall opening formed therein, and the burner is mounted on an exterior side portion of the water heater. The immersion heating structures used in this approach tend to be rather complicated from a manufacturing standpoint, and the overall heating structure still tends to interfere with the jacket insulation forming process. Additionally, the heat input to the tank water tends to be undesirably concentrated in a vertically intermediate portion of the tank interior.
Yet another approach attempted in the prior art, illustrated in the 1945 U.S. Pat. No. 2,543,835 to Dewey, is to provide a down fired, multi-pass immersion heating structure in which the hot combustion gases downwardly enter and then upwardly exit the tank interior. The Dewey immersion heating structure is removably secured to the upper end of a liquid heating vessel and comprises a spaced pair of vertical inlet and discharge flues connected at their lower ends to rectangular header boxes that are joined by a plurality of rectangularly cross-sectioned horizontal flues. The upper end of the inlet flue is connected to a burner structure, and the upper end of the discharge flue is connected to the inlet of a suction fan.
Despite its top burner mounting and multi-pass combustion gas flow routing, the Dewey immersion heater structure is not well suited for use in modern mass produced residential or commercial water heaters for a variety of reasons. For example, the headered immersion heater structure is of a relatively complicated (and thus expensive) configuration requiring that several welding steps be performed to operatively interconnect the necessary cylindrical inlet and discharge flues, the rectangular headers, and the multi-channel horizontal bottom flue structure. Also, the multi-piece nature of the Dewey immersion heater structure undesirably places a series of heater joints within the liquid vessel. Furthermore, the heater structure is designed to be removed for cleaning, thereby requiring a dual flanged interconnection between a top end portion of the liquid vessel and the flat top plate to which the immersion heater structure is secured.
It can be seen from the foregoing that a need exists for an improved fuel fired water heater that is simpler, less expensive to manufacture and more fuel efficient than conventional upflow water heaters, and that also eliminates or at least substantially reduces the problems, limitations and disadvantages typically associated with prior art alternatives to upflow water heaters. It is accordingly an object of the present invention to provide such an improved fuel fired water heater.